Here:
"And I'm going to work together with Congress to say, OK, what -- what are the various ways we could bring down deductions, for instance? One way, for instance, would be to have a single number. Make up a number, $25,000, $50,000. Anybody can have deductions up to that amount. And then that number disappears for high-income people. That's one way one could do it. One could follow Bowles-Simpson as a model and take deduction by deduction and make differences that way. There are alternatives to accomplish the objective I have, which is to bring down rates, broaden the base, simplify the code, and create incentives for growth."
You can read Martin Feldstein's argument for capping deductions, here, from which this excerpt:
Limiting the revenue loss from the itemized deductions and the exclusion of employer payments for health insurance to two percent of each individual’s adjusted gross income would raise more than $275 billion at current income levels and more than $3 trillion over the next decade.